Switched mode power supply and method of production

ABSTRACT

A switched mode power supply allowing a half bridge converter to be use alone or in combination with another converter to form a full bridge converter. A common controller may be used for either half bridge or full bridge configurations. The modular approach simplifies design for a range of power supplies and reduces costs.

FIELD OF THE INVENTION

This invention relates to a switched mode power supply and a method ofproducing a full bridge converter from two half bridge converters. Thedesign allows a standard half bridge converter to be use alone or incombination with another converter to form a full bridge converter.

BACKGROUND OF THE INVENTION

Traditional AC/DC switched mode power supplies for thetelecommunications industry follow a general design based around twoindividual cascaded power converters. The first power conversion stagetypically performs the function of Power Factor Correction (PFC) and isalmost exclusively based around a non-isolated boost converter topology.The second power conversion stage performs the functions of galvanicisolation and voltage transformation/control. A number of distinctlydifferent circuit topologies have been successfully employed to performthe second stage of conversion. Some of the topologies that are commonlyused are: Single switch forward converter, 2-switch forward converter,Half-bridge converter, and the Full-bridge converter. These convertersmay either employ hard or soft switching of the power switchingtransistors and/or diodes and all references to converters in thisspecification shall encompass either switching technique.

The different power converter topologies form a spectrum of designsolutions with the simpler topologies best satisfying the requirementsfor low parts count in small power supplies, and the more complextopologies justifying their added complexity due to their improvedperformance in large power supplies.

A power supply manufacturer who provides a range of different powerlevel solutions will therefore tend to face the need to develop a numberof different product solutions, usually based on a range of differentpower conversion topologies. Each of these design solutions has itsintendant engineering costs: design validation, compliance testing,production support, and product support. Any engineering solution thatcould result in a simple scalable product design can reduce thisengineering cost as well as gaining volume-manufacturing efficiencies.

It is an object of this invention to provide a design that reduces thecost of design and provides a relatively simple and cost effective rangeof power supplies or to at least provide the public with a usefulchoice.

SUMMARY OF THE INVENTION

According to a first aspect there is provided a switched mode powersupply including:

-   -   first and second half bridge converters interconnected to form a        full bridge converter; and    -   a control circuit for controlling the first and second        controllers.

According to a further aspect there is provided a method of producing aswitched mode power supply comprising:

-   -   a. providing two separate half bridge converters;    -   b. providing a control circuit;    -   c. connecting the half bridge converters so as to form a full        bridge converter; and    -   d. connecting drive outputs of the control circuit to respective        switches of the half bridge converters in such a manner that it        drives the converters as a full bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which are incorporated in and constitute partof the specification, illustrate embodiments of the invention and,together with the general description of the invention given above, andthe detailed description of embodiments given below, serve to explainthe principles of the invention.

FIG. 1 shows a two stage power supply with a boost first stage followedby a half bridge converter; and

FIG. 2 shows a power supply having a full bridge converter formed bycombining two power supplies as shown in FIG. 1.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a power supply 1 having a boost converter stage 2 followedby a half bridge converter 3. Switches 4 and 5 of half bridge converter3 and switch 6 of boost converter 2 are driven by control circuit 7. Thedrive signals from control circuit 7 to switches 4 and 5 may be isolatedby devices such as signal isolating transformers etc. as is known in theart. Control circuit 7 monitors output voltage and current and controlsswitches 4 and 5 so as to bring the monitored output current and voltagetowards desired values. Switches 4 and 5 are driven by signals which arethe logical inverse of one another so that they are alternately switchedon and off. Input voltage and/or current may also be monitored andswitch 6 may be controlled so as to achieve power factor correction(PFC).

The primary coil 8 of transformer 9 is connected between the output ofthe half bridge and the mid voltage point defined between capacitors 10and 11. The output of transformer 9 is then rectified by rectifier 12and filtered by the filter formed by inductor 13 and capacitor 14.

Where a higher power application is required two such power suppliescould be connected in parallel (i.e. AC inputs connected in parallel andDC outputs connected in parallel). However, this would require twocontrol circuits and would not enjoy the benefits of full bridgeoperation.

FIG. 2 shows an arrangement in which two converters of the type shown inFIG. 1 are connected together so as to form a full bridge converteroutput stage. Power supplies 15 and 16 are interconnected so as to forma full bridge converter with both converters driven by common controlcircuit 17.

The AC inputs to the converters are connected in parallel by lines 18and 19. The outputs are connected in parallel by lines 29 and 30. The DCrails of the converters are connected in parallel by lines 20 and 28.The switches 6 a and 6 b of the boost converters are commonly driven bycontrol circuit 17. Top switch 4 a and bottom switch 5 b are commonlydriven via lines 23 and 24 by a non-inverting output of control circuit17. Bottom switch 5 a and top switch 4 b may be commonly driven vialines 25 and 26 of control circuit 17.

Power supplies 15 and 16 may be in the form of PCBs stacked on top ofone another with lines 18, 19, 20, 27, 28, 29 and 30 in the form ofconductive pins soldered to commonly located points on each PCB. Lines21, 22, 23, 24, 25 and 26 may be in the form of flexible wires fromcontrol circuit 17 to respective PCBs 15 and 16. Alternatively controlcircuit 17 could be integrally formed on one of the PCBs 15 or 16 withlands formed on the PCB to facilitate the connection of conductors to aPCB without a control circuit.

Instead of connecting the lower ends of primary windings to the junctionof the capacitors those ends are interconnected via line 27. The seriesconnection of primary windings 8 a and 8 b across the outputs of theswitches 4 a and 5 a and 4 b and 5 b and the arrangement for drivingthose switches provides full bridge operation. This results in improvedoutput waveforms and requires only a single control circuit, reducingcost and complexity. This integrated design also allows all componentsto be housed in a single enclosure using a single fan. This approachallows a single power supply design to be used for different power levelapplications; reducing design cost and simplifying manufacture andinventory management. Although this concept has been described inrelation to a two stage AC/DC power supply it is equally applicable to asingle stage power supply.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin detail, it is not the intention to restrict or in any way limit thescope of the appended claims to such detail. Additional advantages andmodifications will readily appear to those skilled in the art.Therefore, the invention in its broader aspects is not limited to thespecific details, representative apparatus and method, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departure from the spirit or scope of theApplicant's general inventive concept.

1-11. (canceled)
 12. A switched mode power supply including: first andsecond discrete half bridge converters interconnected to form a fullbridge converter; and a control circuit for controlling the first andsecond controllers.
 13. A switched mode power supply as claimed in claim12 wherein the outputs of each converter are connected to seriesconnected primary windings of respective output transformers.
 14. Aswitched mode power supply as claimed in claim 12 wherein the first andsecond half bridge converters are provided on separate circuit boards.15. A switched mode power supply as claimed in claim 12 wherein thecontrol circuit is provided on a separate circuit board.
 16. A switchedmode power supply as claimed in claim 14 wherein the control circuit isprovided on a separate circuit board.
 17. A switched mode power supplyas claimed in claim 12 wherein a boost stage is provided prior to eachhalf bridge converter.
 18. A switched mode power supply as claimed inclaim 14 wherein a boost stage is provided prior to each half bridgeconverter.
 19. A switched mode power supply as claimed in claim 15wherein a boost stage is provided prior to each half bridge converter.20. A switched mode power supply as claimed in claim 16 wherein a booststage is provided prior to each half bridge converter.
 21. A switchedmode power supply as claimed in claim 12 wherein the control circuitmonitors the output voltage and current of the power supply and controlsswitching of the half bridge converters to achieve a desired outputvoltage and current.
 22. A switched mode power supply as claimed inclaim 14 wherein the control circuit monitors the output voltage andcurrent of the power supply and controls switching of the half bridgeconverters to achieve a desired output voltage and current.
 23. Aswitched mode power supply as claimed in claim 15 wherein the controlcircuit monitors the output voltage and current of the power supply andcontrols switching of the half bridge converters to achieve a desiredoutput voltage and current.
 24. A switched mode power supply as claimedin claim 12 wherein the top switch of the first half bridge converterand the bottom switch of the second half bridge converter are driven bya first drive signal from the control circuit and the bottom switch ofthe first half bridge converter and the top switch of the second halfbridge converter are driven by a second drive signal from the controlcircuit, wherein the second drive signal is the logical inverse of thefirst drive signal.
 25. A switched mode power supply as claimed in claim14 wherein the top switch of the first half bridge converter and thebottom switch of the second half bridge converter are driven by a firstdrive signal from the control circuit and the bottom switch of the firsthalf bridge converter and the top switch of the second half bridgeconverter are driven by a second drive signal from the control circuit,wherein the second drive signal is the logical inverse of the firstdrive signal.
 26. A switched mode power supply as claimed in claim 15wherein the top switch of the first half bridge converter and the bottomswitch of the second half bridge converter are driven by a first drivesignal from the control circuit and the bottom switch of the first halfbridge converter and the top switch of the second half bridge converterare driven by a second drive signal from the control circuit, whereinthe second drive signal is the logical inverse of the first drivesignal.
 27. A switched mode power supply as claimed in claim 12including rectifiers connected to the outputs of the secondary windingsof the transformer.
 28. A method of producing a switched mode powersupply comprising: providing two discrete half bridge converters;providing a control circuit; connecting the half bridge converters so asto form a full bridge converter; and connecting drive outputs of thecontrol circuit to respective switches of the half bridge converters insuch a manner that it drives the converters as a full bridge.
 29. Amethod as claimed in claim 28 including the step of connecting theoutputs to series connected primary windings of respective outputtransformers.
 30. A method as claimed in claim 28 including the step ofconnecting the top switch of the first half bridge converter and thebottom switch of the second half bridge converter to a first drivesignal output of the control circuit and the bottom switch of the firsthalf bridge converter and the top switch of the second half bridgeconverter to a second drive signal output of the control circuit,wherein the second drive signal is the logical inverse of the firstdrive signal.
 31. A method as claimed in claim 29 including the step ofconnecting the top switch of the first half bridge converter and thebottom switch of the second half bridge converter to a first drivesignal output of the control circuit and the bottom switch of the firsthalf bridge converter and the top switch of the second half bridgeconverter to a second drive signal output of the control circuit,wherein the second drive signal is the logical inverse of the firstdrive signal.